New therapies have been developed for treatment of hereditary angioedema, a disorder of the complement system with a previously high mortality. We have developed, with the Red Cross, a purified C1 esterase inhibitor preparation that reverses the blood biochemical abnormality and, also, ends acute attacks of disease. We have developed chronic therapy which leads to clinical cure of this disease, and often, causes complete correcton of the biochemical abnormality in this genetically controlled deficiency state. Anaylsis of the mechanism of correction has led to a unified genetic hypothesis for the origin of the disease. We have provided definitive data on the incidence of drug toxicity in this disease and showed that danazol predisposes certain patients to develop insulin resistant diabetes.